The drive train is responsible for actuating the actual valve body on the radiator. This is typically done by driving a threaded pin, which in turn pushes against the pin of the valve body.

In the image above, the grey knurled collar to the right of the image has a thread of M30x1.5 making it suitable for attachment to Danfoss RA, RAV and RAVL valves. The driven pin is at this end of the assembly.

To the centre of the image, a motor can be seen with 2 wires leaving to the brains of the TRV.

We were lucky enough to find documentation of how the drive unit is constructed shown below.

I’d like to highlight the black gear wheel with three white spots in stage 12 (bild 12) above, this along with the Optoreflexkoppler, the small black chip in stage 16 (bild 16), allows the TRV brains to keep track of the valve position and learn the limits of travel of the radiator valve body itself.